Patent GB-648867-A (GB)
Title: Preselector
IPC: G05D3/12
Filed: 1948-02-20
Abstract: 648,867. Electric selective signalling. GUARDIAN ELECTRIC MANUFACTURING CO. Feb. 20, 1948, No. 5151. Convention date, March 22, 1943. [Class 40 (i)] A preselector for controlling powerdriven follow-up mechanism comprises a stepper gear adapted to be clutched to a control knob, by axial movement of the latter, and then rotatably adjusted therewith in either direction to a selected position. Release of the control knob then disengages the stepper gear and at the same time completes the circuit to the motor drive for the controlled member. A cam driven by the motor operates a pulsing circuit for the appropriate one of a pair of electromagnets which steps the stepper gear back to its neutral position, when the motor circuit is broken but only after the motor has advanced sufficiently to break the pulsing circuit. The invention is applicable to the control of trim tabs for aircraft, guns, machines &c. Transmitter construction. As shown, the control knob 50, Fig. 1, is secured by a transparent disc 45 to an annular indicator 46 fixed to a cup-shaped member 43 which, with a selector gear 76 is fixed to a rotatable sleeve 20. The knob is normally held against rotation by a stationary locking pin 80, Fig. 2, engaging in one of the teeth of the selector gear. Pushing the knob inwards (i.e. axially) releases the selector gear from the locking pin, after which the knob is rotated in either direction to a desired setting, and then released, whereupon it is returned axially by leaf-springs 77 to its original axial position, where it is again locked by the pin 80, the new setting being indicated by a fixed index mark 40, Fig. 3, against the graduated dial 46. A stepper gear-wheel 82, identical with the selector gear 76, is mounted concentrically therewith, and is locked to the selector gear during rotary setting thereof by a pin 86 on the selector gear engaging between teeth on the stepper gear, the stepper gear being released when the selector gear is retracted axially upon release of the control knob. The inward axial movement of the control knob 50 also opens a main switch 69 through a central shaft 55 nested within a tubular shaft 21 carrying the stepper gear, so that the motor and stepping circuits cannot be energized until the control knob is released after setting to its new position when the main switch closes as the knob retracts axially. The main switch may also be opened to render the apparatus inoperative by depressing a further knob 57, axially slidable within the control knob 50 against the action of a spring 59, the knob 57 being held in the " open " position by rotating it through 90 degrees. A cam 120 on shaft 21 rotates with the stepper gear and has diametrally opposite shoulders 120a, Fig. 10, coacting with spring members 116 pivoted at 115, to limit the rotation of the stepper gear in either direction to slightly less than 180 degrees from the zero or normal position. The spring members are also adapted to operate, respectively, pairs of switches 106, 107 or 108, 109, Fig. 7, in the off-normal position of the cam, the pair actuated being dependent on the direction of setting of the stepper gear. After a setting operation the shaft 21 is returned to the zero position by one of two stepper magnets 96, 97, Figs. 1, 2, acting through armatures 96c, 97c on the stepper gear 82, the rotary position of which is indicated by an index 38 on a dial 37 carried by shaft 21 and visible through the disc 45. The stepper gear coacts with a spring-biassed roller detent 88 to ensure precise positioning thereof. The operative magnet also reciprocates a respective link 126, Fig. 10, slidably in a slot in the respective member 116 and functioning to maintain operated the actuated pair of switches 106, 107 or 108, 109 as the stepper gear is returned to the zero position until the operative stepper magnet has become de-energized. Circuit arrangements, Fig. 13. When the control knob 50 is released after rotation to a new setting, the motor armature 154 is energized in the appropriate sense over the switches 107 109, one of which has been actuated to offnormal by cam 120 as above described. The motor drives the controlled member and also a cam 151 which pulses the appropriate stepping magnet 96, 97 over the associated actuated switch 106 or 108 until the stepper gear has returned to normal. The motor circuit is, however, maintained by the operative link 126 as above described until the cam 151 has advanced sufficiently to open the pulsing circuit, when the operative link 126, Fig. 10, drops to permit the actuated switches 106-109 to revert to normal and de-energize the motor. Limit switches 155, 156 ensure that the normal range of movement of the controlled member is not exceeded. Operation of either limit switch causes rapid dynamic braking to rest of the motor.